Pb and Pu in the Northeast Water Polynya, Greenland: particle dynamics and sediment mixing rates

Distributions of the radionuclides ²¹⁰Pb and ^239,240Pu in sediment cores from the Northeast Water Polynya, Greenland, showed that these nuclides reached depths of 5–15 cm by particle mixing and sediment accumulation. End-member average values of the particle mixing coefficient and sediment accumulation rate were 0.13 cm² y⁻¹ and 0.06 cm y⁻¹, obtained from the ²¹⁰Pb profiles by assuming that each process is dominant relative to the other. Both ²¹⁰Pb and ^239,240Pu were measured on four cores; using the Pu data to constrain mixing rates produced corrected sediment accumulation rates that were 20–80% of the values calculated by neglecting mixing. Organic carbon burial in the polynya sediments was ≤0.4 mmol m⁻² d⁻¹, based on measured POC values at depth in the sediments and sediment accumulation rates corrected for mixing. This value is about 1% of the independently measured POC flux leaving the euphotic zone and compares with benthic carbon remineralization rates of 7% calculated by others from O₂ uptake in the sediments.The inventories of excess ²¹⁰Pb in the sediments ranged from 6 to 28 dpm cm⁻². Relative to the atmospheric input of ²¹⁰Pb and in situ production from decay of ²²⁶Ra, approximately 5 dpm cm⁻² of ²¹⁰Pb was being removed from the water column. The difference between the removal from the water column and sediment inventories suggests a net import of ²¹⁰Pb to the polynya. This may occur by input of dissolved ²¹⁰Pb from offshore waters or by input of ²¹⁰Pb carried by sea ice. Particulate matter in land-derived fast ice adjacent to the polynya contained 330 ± 14 dpm of excess ²¹⁰Pb g⁻¹. If particles transported in sea ice are comparable to those extracted from fast ice, then sea ice transport into the polynya followed by melting may be an important source of excess ²¹⁰Pb to the area. Fast ice also may contribute ²¹⁰Pb if portions break off and melt within the polynya, as occurred in 1993.     

舰船回转过程中内、外侧螺旋桨负荷变化规律的新现象

在许多教科书中,螺旋桨推进双桨船在回转过程中内、外螺旋桨负荷变化规律均有如下叙述:回转过程中内侧螺旋桨负荷远大于外侧螺旋桨负荷.这个结论也被某些实船试验结果所证实.但新近完成的某双桨船的回转试验的多个实测结果表明:外侧螺旋桨负荷远大于内侧螺旋桨负荷.在上世纪90年代国内有人已发现过这一新现象,但当时无人记录和分析以进行研究.本文报告和分析了这一新现象.文章首先简要回顾了以往教科书和某些实船试航回转过程中内、外桨负荷变化规律;然后介绍了某新船回转试验的实测结果,论述了实测结果的可信性.本文着重探讨了导致这一新现象的主要原因,如船体形状、船的运动、内外螺旋桨的运动、桨与船的相互作用和桨与桨的相互作用等.     

New-Level VR Marine Training System

Marine simulator is a valuable and effective medium for maritime education and training and is becoming widespread to foster the qualified and competent personnel for working in the maritime industry.However,many problems with most marine simulation systems today limit their pervasive use:the limited accessibility,immobility,the high expenditure,the long develop- meat cycle,and the difficult maintenance etc.A web-based maritime training environment is proposed in this paper as a new ma- rine training level,which fully combining web technology,VR,high fidelity simulation,and e-learning tools to create a more cost- effective and flexible training environment still with very realistic and high-interactive simulation characteristics,the system will provide a consistent and more flexible training medium for improving maritime education and training.     

地震作用下高速铁路桥梁的动力响应及行车安全性研究

将桥梁在地震作用下的运动方程和车辆振动方程，通过桥梁子系统与车辆子系统间的非线性轮轨接触关系联系起来，建立可考虑多点激励与行波效应的车桥系统地震反应动力学分析模型。以某高速铁路连续梁桥为例，对非一致地震激励下桥梁结构的动力响应及桥上车辆运行安全性进行研究，提出确保地震发生时高速列车在桥上安全运行的临界速度限值，可供实际工程设计时参考。     

海工耐久混凝土氯离子渗透性能的影响因素及其扩散系数的早期推定

大规模海工耐久混凝土在国内应用很少,各种影响因素对其影响作用不甚明了,通过正交设计的方法研究各影响因素对耐久性的影响,对指导配合比设计和施工过程质量控制具有积极的意义。     

沉箱箱壁计算分析和局部优化

采用结构计算程序AN SY S,对北方某港拟建的15万吨级矿石转水码头大直径圆沉箱箱壁进行了计算。对桥梁计算中通用的影响线加载程序进行修改,编制成适用于卸船机荷载的动态规划程序,并嵌入结构分析程序中,计算出最不利组合工况下的沉箱箱壁受力;同时参考AN SY S拓扑优化结果,对沉箱消浪孔形式和布置位置等进行了调整,计算分析后给出了受力性能更为合理的细部构造布置。     

利用Boussinesq方程对作用于大直径圆筒结构上的波浪力进行数值模拟

采用求解Beji和Nadaoka改进的Boussinesq方程,模拟了波浪在多个串连大圆筒结构前的反射,得到了作用于圆筒结构上的波浪力。空间离散采用有限元方法,可以较好地适应圆筒结构表面形成的复杂边界形状。数值模拟结果与公开发表的物理模型试验成果进行了比较,符合较好。     

声表面波气体传感器器件的设计

论述了声表面波气体传感器器件的结构设计及设计参数的选择,设计了ST和AT不同切向的石英晶体材料做压电基片材料的三种振荡器,通过电性能参数的测试,比较了三种振荡器的性能优劣。     

船舶电站物理仿真实验装置典型故障分析

阐述了最新研制开发的船舶电站物理仿真实验装置的仿真原理,分析并排除了该装置调试运行过程中出现的典型故障,为电站操作人员提供参考。     

基于马尔可夫链的极值波高预测

本文研究了由日最大波高系列估算设计极值波高时，相邻日最大波高间的相关性对极值预测的影响，从日最大波高系列遵从马尔可夫链的假定出发，考虑到国内外经常采用对数一正态分布的韦布尔分布拟合波高长期分布的现实，本文用解析法求解了对数一正态分布情况下的极值预测。同时，对解析法难以求解的非正态随机变量情况（如韦布尔分布），用计算机随机模拟方法求解其极值预测，用上述两种方法对北大西洋和北海有关日最大波高系列的预测